CN111902168A

CN111902168A - Intravascular blood pump

Info

Publication number: CN111902168A
Application number: CN201980020590.5A
Authority: CN
Inventors: F·基尔霍夫; T·西斯; W·克尔霍夫斯
Original assignee: Abiomed Europe GmbH
Current assignee: Abiomed Europe GmbH
Priority date: 2018-03-23
Filing date: 2019-03-21
Publication date: 2020-11-06
Also published as: CN116747424A; SG11202008947SA; US11951299B2; AU2019237196A1; AU2019237194A1; IL275978A; CN111971079B; US20230057161A1; US20210113825A1; IL277176A; JP2021519118A; US20210015981A1; JP2021518199A; SG11202006725TA; JP2024026644A; EP3542837B1; CN116747425A; EP3768343A1; KR20200135446A; CN111971079A

Abstract

An intravascular blood pump has a rotatable shaft (25) carrying an impeller (34) and a housing (20) having an opening (35), the shaft extending through the opening (35), the impeller being positioned outside the housing. The shaft and the housing have surfaces (25A, 33A) forming a circumferential slit converging towards the impeller-side end of the slit and having a minimum slit width preferably not more than 5 μm, more preferably not more than 2 μm.

Description

Intravascular blood pump

Technical Field

The invention relates to an intravascular blood pump, in particular a percutaneously insertable blood pump, for supporting a blood circulation in the body of a human being or optionally also an animal. For example, a blood pump may be designed to be inserted percutaneously into the femoral artery and to be guided through the vascular system of the body, for example to support or replace pumping action in the heart.

Background

A blood pump of the type mentioned above is known, for example, from EP 0961621B 1, which has a drive section, a conduit attached to the proximal end of the drive section (which is the end of the drive section closer to the physician or "trailing end" of the drive section) and having a wire extending therethrough for supplying electrical power to the drive section, and a pump section fastened at the distal end of the drive section. The drive section comprises a motor housing having an electric motor arranged therein, wherein a motor shaft of the electric motor protrudes distally out of the drive section and into the pump section. The pump segment in turn comprises a tubular pump housing with an impeller rotating therein, which is seated on the end of the motor shaft protruding from the motor housing. The motor shaft is mounted in the motor housing in two bearings, which are maximally separated from each other to ensure a true, precisely centered guidance of the impeller within the pump housing. Although a radial ball bearing is used for the bearing at the proximal end of the motor housing, the impeller-side bearing (which is the bearing closest to the blood) is constructed as a blood-resistant shaft seal made of polytetrafluoroethylene, which has high hardness and a low coefficient of friction, thereby providing a bearing and at the same time preventing blood from entering the motor housing through such distal bearing. In addition, the cleaning fluid is transmitted through the motor housing and the impeller-side shaft seal bearing, resisting the entry of blood into the motor housing. This is done at a wash fluid pressure higher than the pressure present in the blood.

An improvement of the blood pump mentioned above is disclosed in US2015/0051436 a1 and is shown in figure 2 attached hereto. The impeller-side bearing at the distal end of the motor housing here comprises an axial slide bearing and a radial slide bearing or a combined axial-radial slide bearing, wherein the radial slide bearing replaces the above-mentioned shaft sealing bearing. Accordingly, the cleaning fluid passes through the slits of the impeller-side radial sliding bearing to prevent blood from entering the housing.

Although the invention will be described and preferably used in the context of an intravascular blood pump having a motor of the type mentioned above housed in the housing, the invention is equally advantageously applicable to other types of intravascular blood pumps in which the motor is external to the body of the patient and rotational energy for the impeller is transmitted through the catheter and the housing attached to the distal end of the catheter by means of a flexible rotational drive cable. Furthermore, in this type of intravascular blood pump, the wash fluid typically enters the patient's blood through an opening through which the drive shaft extends.

Heparin, typically mixed into the cleaning fluid, poses a common problem. That is, although the washing fluid flows through the gap formed between the shaft and the opening of the housing, thereby pushing back the blood that tends to enter the housing through such a gap, the entry of the blood into the gap cannot be completely prevented. In particular, some blood may always enter at least the distal section of such a slit. Heparin helps prevent blood from clotting in the crevices or blood adhering to the surface, and thus prevents blockage of shaft rotation. However, physicians often do not want heparin to be administered to a patient's blood via a cleaning fluid. For example, during emergency treatment heparin may be counterproductive in that it prevents the clotting of blood and thus healing or hemostasis. Furthermore, the amount of heparin that is administered to the patient's blood along with the wash fluid is difficult to control for various reasons. In particular, the amount of heparin is often more than the amount desired by the physician. Accordingly, the physician will often prefer to supply heparin to the patient separately from the operation of the blood pump, if and in the required amounts.

Accordingly, there is a need for an intravascular blood pump that can be operated with a cleaning fluid that contains no or at least less heparin, if desired.

Disclosure of Invention

Thus, according to a first aspect of the invention, an intravascular blood pump may comprise a rotatable shaft carrying an impeller and a housing having an opening through which the shaft extends, the impeller being positioned outside the housing, the shaft and housing having surfaces forming a circumferential slit within the opening. This is not different from the prior art discussed above, and the gap may in particular constitute a radial sliding bearing for the shaft. However, in the blood pumps disclosed herein, the slits converge towards the leading or impeller-side end such that the minimum width of the slit is located somewhere within 50% of the length of the slit closest to the impeller-side end of the slit. More preferably, said minimum width is present at least at the impeller-side end of the slot.

The advantage of the slits converging towards the front end or impeller side end or distal end of the slits (these terms having the same meaning) is that the pressure drop created in the cleaning fluid flowing along the length of the slits from the proximal end to the distal end can be kept low compared to the pressure drop in non-converging slits of the same length having said minimum width over the entire length of the slits. More specifically, it is desirable according to the present invention to have a relatively high velocity of the cleaning fluid at the impeller-side end of the slit, which is the side of the slit that is in contact with the blood, to prevent blood from entering the slit. Therefore, the smaller the gap, the better. However, a very small gap along the entire length of the gap requires that the wash fluid be delivered to the blood pump at extremely high pressures. By making the slits converge towards the distal end, a washing fluid pump providing a pressure of, for example, 1 to 1.5bar can be used even with a very small minimum slit width.

For example, a minimum gap of 5 μm in the region of the impeller-side end of the gap may allow the washing fluid to leave the gap at such a high speed that substantially no blood will enter the gap. Accordingly, it becomes possible to clean the crevices using a cleaning fluid having relatively little or even no heparin.

A minimum gap width of 5 μm or less also provides a physical barrier to the entry of red blood cells into the gap to some extent, due to the relatively large blood cell diameter of approximately 8 μm. However, since the thickness of blood cells is only approximately 2 μm, it is preferable that the minimum slit width is 2 μm or less. As stated, due to the smaller gap width, the cleaning fluid flows through the gap at a higher velocity, thereby pushing the blood back out of the gap with the highest possible kinetic energy.

In the case of a minimum gap width which is limited in practice to the impeller-side end of the gap, i.e. to an infinitely small short section of the length of the gap, this may lead to increased wear in the individual sections of the gap. Thus, according to a preferred embodiment, the section of the slit having the smallest slit width may extend over 50% or less, preferably 30% or less, but preferably not less than 20% of the length of the slit to keep the wear low. The length of such a segment may be in the range between 0.1 and 0.7mm, more preferably between 0.2 and 0.4 mm.

The convergence of the gap may be achieved by tapering one or both of the surfaces forming the gap, i.e. the tapered outer surface of the gap formed by the inner surface of the opening through the wall of the housing and the tapered inner surface of the gap formed by the surface of the shaft. The tapering of the outer surface of the slot means a decrease in the diameter of the wall opening towards the impeller-side end of the slot, and the tapering of the inner surface of the slot means an increase in the diameter of the shaft towards the impeller-side end of the slot. It is preferred to provide a taper in the surface of the shaft, whereas the opening constituting the outer boundary of the slit may be cylindrical, because of ease of manufacture.

The preferred length of the slit is in the range from 1 to 2mm, preferably 1.3 to 1.7mm, while the minimum slit width may be 5 μm or less, preferably 4 μm or less, more preferably 3 μm or less, and most preferably 2 μm or less. The maximum slot width is typically located at the end of the slot opposite the impeller-side end of the slot and amounts to 15 μm or less, preferably 10 μm or less, more preferably 8 μm or less, and most preferably 6 μm or less. Most preferred are converging slits having a maximum slit width of about 6 μm and a minimum slit width of 2 μm or less.

Furthermore, the slit may converge continuously, in particular linearly, over at least a portion of its length until the slit has its minimum width.

In a particularly preferred embodiment, at least one of the two surfaces forming the circumferential slot is made of a material having a thermal conductivity λ ≧ 100W/mK.

By making the surface from a material with a relatively high thermal conductivity, the temperature in the gap can be kept low, preferably at 55 ℃ or lower, thereby preventing denaturation of any fibrin in the plasma that may enter the gap despite all efforts.

The material of one or more surfaces forming the gap having a thermal conductivity of 100W/mK may be sufficient to conduct heat away from the gap and thus maintain the temperature within the gap at 55 ℃ or less. However, the thermal conductivity is preferably at least 130W/mK, more preferably at least 150W/mK and most preferably at least 200W/mK.

In order to transfer heat away from the gap into the blood, it is preferred that the gap-forming surface is in thermally conductive contact with the blood flow flowing through the pump. According to thermodynamics, flowing blood removes heat faster than non-flowing blood. The faster the blood flows, the more heat can be removed by conductive heat transfer. The blood flow rate through the pump is typically higher than the blood flow rate outside the pump. Hereby, for example, heat generated in the gap and heating the surfaces forming the gap may be further conducted from the surface of the shaft through the shaft body into the impeller at the end of the shaft and from there into the blood flowing along the impeller. However, since the distance for heat to flow in the axial direction through the shaft body and further through the impeller into the blood is relatively long, it is more preferred to conduct heat away from the slit (additionally or only) in the radial direction, i.e. through the radially outer surface forming the slit. Carrying heat away in the radial direction is preferred not only because of the relatively short radial distance for heat to flow from the slit to the flowing blood, but also because it is easier to increase the heat conducting area through which heat can be conducted in the radial direction compared to the heat conducting cross-sectional area of the shaft body through which heat can be conducted in the axial direction. I.e. the cross-sectional area A of the shaft body_{Axial direction}Is A_{Axial direction}＝πd²/4 and the cross-sectional area A of the radially outer surface forming the slit_{Radial direction}Is A_{Radial direction}Pi dl. Thus, the diameter of the slit is increased (e.g. to d ═ 1)mm) is the cross-sectional area A of the radially outer surface forming the gap_{Radial direction}Four times higher than the sectional area A of the main body of the shaft_{Axial direction}. Furthermore, increasing the length (l) of the slit is only for the cross-sectional area A of the radially outer surface forming the slit_{Radial direction}Having a positive influence and having a cross-sectional area A of the shaft body_{Axial direction}There was no effect at all. In any case, the slit should preferably be long and have a large diameter. However, because a large diameter can counter the amount of heat generated in the gap, the diameter of the gap should not be too large (preferably d ≦ 1 mm). Most preferably, the thermal conductivity of both the surfaces forming the gap is high, at least 100W/mK, and in thermally conductive contact with the blood flow.

Such thermally conductive contact may be direct or indirect. Direct heat-conducting contact can be achieved if the respective heat-conducting surfaces forming the gap constitute a part of a structural element which is entirely made of said heat-conducting material and which is in direct contact with the blood flow through the pump when the intravascular blood pump is operating in the blood vessel of the patient. This may be the case when the shaft and impeller form an integral part formed of one thermally conductive material and/or when the distal end of the housing forming the through-hole for passage of the shaft is an integral part made of a thermally conductive material.

Alternatively, an indirect thermally conductive contact can be achieved if one or more of the gap-forming surfaces respectively constitute a part of a structural element which is entirely made of said thermally conductive material and has at least one further surface which is thermally conductively connected to a separate thermally conductive element which is in direct contact with the flowing blood or in indirect thermally conductive contact with the flowing blood via the one or more further thermally conductive elements when the intravascular blood pump is running in the blood vessel of the patient, so that heat from the one or more gap-forming surfaces can be dissipated into the flowing blood by thermal conduction. Of course, the heat conducting element itself should have a high thermal conductivity, preferably higher than the preferred thermal conductivity of the one or more surfaces forming the gap, i.e. higher than 100W/mK, preferably higher than 130W/mK, more preferably higher than 150W/mK and most preferably higher than 200W/mK.

Since the surfaces forming the slits may preferably constitute radial sliding bearings for the shaft, the surfaces should have a very small surface roughness, preferably a surface roughness of 0.1 μm or less. Although such a surface roughness may be obtained using a diamond-like carbon coating (DLC), as proposed in US2015/0051436 a1 as a coating for a shaft, it is not possible using current techniques to apply a DLC coating so precisely that a gap width of 2 μm or less can be achieved over the length of the gap. It is therefore preferred to manufacture one or more of the crevice-forming surfaces from a different material and/or by a different method than DLC, most preferably from a ceramic material, in particular from a sintered ceramic element. That is, preferably, the heat conducting surface is not a coating on the structural element, but a surface of one or more structural elements, i.e. one or more elements of the assembled pump.

One common problem with ceramics is that ceramic materials typically have very low thermal conductivity. Zirconium oxide (ZrO) as mentioned, for example, in US 2015/0051436A 1₂) Has a thermal conductivity of only 2.5 to 3W/mK. Alumina (Al)₂O₃) Is a well-known ceramic having a relatively high thermal conductivity of 35 to 40W/mK, but which is still substantially lower than that of metals such as copper. One of the few ceramics with substantially higher thermal conductivity is silicon carbide (SiC). Silicon carbide of a typical process has a thermal conductivity between 100W/mK and 140W/mK, but silicon carbide with higher thermal conductivity is also useful. Pure silicon carbide has a thermal conductivity of 350W/mK. Unlike other ceramics, silicon carbide is very brittle and therefore difficult to handle. Which can be easily broken during manufacture and assembly. However, due to its good heat capacity, silicon carbide is the preferred material for the purposes of the present invention for at least one of the surfaces forming the gap, preferably the radially outer surface of the gap, and, because of its brittleness, is not the preferred material for the shaft. Thus, the respective surface or the entire structural element forming such a surface comprises or preferably consists of silicon carbide.

If silicon carbide forms one surface of the sliding bearing, the mating opposite surface of the sliding bearing may be of substantially any other type of material, in particular any other type of ceramic material. The preferred ceramic material for each of the other surfaces is Alumina Toughened Zirconia (ATZ) because of its high durability, yet it has a thermal conductivity of only 25W/mK. It is therefore preferred to make the shaft from ATZ and the sleeve from SiC in which it is sleeved so that heat can easily be conducted radially outward from the gap out into the flowing blood.

Drawings

Hereinafter, the present invention will be explained by way of example with reference to the accompanying drawings. The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

fig. 1 is a schematic diagram of an intravascular blood pump prior to being inserted into the left ventricle, with its inflow cannula positioned in the left ventricle,

figure 2 is a schematic longitudinal cross-section of an exemplary prior art blood pump,

FIG. 3 is an enlarged view of a portion of the blood pump of FIG. 2, however, having a configuration in accordance with a preferred embodiment of the present invention, and

fig. 4A to 4I are enlarged partial views of the distal radial bearing of the pump, showing variations of the converging circumferential slits.

Fig. 1 shows the use of a blood pump for supporting the left ventricle in this particular embodiment. The blood pump comprises a catheter 14 and a pumping device 10 attached to the catheter 14. The pumping device 10 has a motor section 11 and a pump section 12, which are arranged coaxially behind one another and result in a rod-shaped form of construction. The pump segment 12 has an extension in the form of a flexible suction hose 13, the suction hose 13 often being referred to as a "cannula". An impeller is provided in the pump section 12 to induce a blood flow from the blood flow inlet to the blood flow outlet, and the rotation of the impeller is induced by an electric motor arranged in the motor section 11. The blood pump is placed so that it is mainly located in the ascending aorta 15 b. The aortic valve 18 becomes in the closed state against the outside of the pump segment 12 or its suction hose 13. A blood pump with a forward suction hose 13 is advanced through a forward catheter 14 into the position shown, optionally with a guide wire. In doing so, the suction hose 13 runs in reverse through the aortic valve 18, so blood is sucked in through the suction hose 13 and pumped into the aorta 16.

The use of the blood pump is not limited to the application shown in fig. 1, the application shown in fig. 1 only relating to a typical example of the application. Thus, the pump may also be inserted through other peripheral vessels, such as the subclavian artery. Alternatively, a reverse application to the right ventricle may be envisaged.

Fig. 2 shows an exemplary embodiment of a blood pump according to the prior art US2015/0051436 a1, which is likewise suitable for use in the context of the present invention, except that according to the present invention a rounded front end portion marked with an "I" is used as a modification, a preferred embodiment of such a modification being shown in fig. 3. Accordingly, the motor segment 11 has an elongated housing 20, in which elongated housing 20 the electric motor 21 can be accommodated. The stator 24 of the electric motor 21 may typically have a number of circumferentially distributed windings and a magnetic return path 28 in the longitudinal direction. The magnetic return path 28 may form an outer cylindrical sleeve of the elongated housing 20. The stator 24 may surround a rotor 26 connected to a motor shaft 25 and consist of permanent magnets magnetized in the active direction. The motor shaft 25 may extend over the entire length of the motor housing 20 and protrude distally out of the latter through the opening 35. Where it carries an impeller 34 with pump vanes 36 projecting therefrom, the impeller 34 being rotatable within a tubular pump housing 32, the tubular pump housing 32 being rigidly connectable to the motor housing 20.

The proximal end of the motor housing 20 has a flexible conduit 14 sealingly attached thereto. A cable 23 for supplying power to the electric motor 21 and controlling the electric motor 21 may extend through the conduit 14. Additionally, a purge fluid line 29 may extend through the conduit 14 and penetrate the proximal end wall 22 of the motor housing 20. The cleaning fluid may be fed into the interior of the motor housing 20 through a cleaning fluid line 29 and exit through an end wall 30 at the distal end of the motor housing 20. The purge pressure is selected such that it is higher than the existing blood pressure to thereby prevent blood from penetrating into the motor housing, between 300 and 1400mmHg depending on the application.

As mentioned above, the same cleaned seal may be combined with a pump driven by a flexible drive shaft and a remote motor.

Upon rotation of the impeller 34, blood is drawn through the distal opening 37 of the pump housing 32 and is transported rearwardly in the axial direction within the pump housing 32. Through a radial outlet opening 38 in the pump housing 32, the blood flows out of the pump segment 12 and further along the motor housing 20. This ensures that the heat generated in the motor is carried away. It is also possible to operate the pump segments using a reverse direction of delivery, with blood being drawn along the motor housing 20 and exiting from the distal opening 37 of the pump housing 32.

The motor shaft 25 is mounted in

radial bearings

27, 31 at the proximal end of the motor housing 20 on the one hand and in

radial bearings

27, 31 at the distal end of the motor housing 20 on the other hand. The radial bearing, in particular the radial bearing 31 in the opening 35 at the distal end of the motor housing, is designed as a plain bearing. Furthermore, the motor shaft 25 is also mounted axially in the motor housing 20, and the axial bearing 40 is likewise designed as a plain bearing. The axial sliding bearing 40 is used to receive the axial force of the motor shaft 25 acting in the distal direction when the impeller 34 transports blood from the distal end to the proximal end. If a blood pump is used for conveying blood also or only in the reverse direction, a corresponding axial plain bearing 40 can be provided (also or only) in a corresponding manner at the proximal end of the motor housing 20.

Fig. 3 shows in more detail the portion marked with an "I" in fig. 2, however structurally modified according to a preferred embodiment of the invention. The radial slide bearing 31 and the axial slide bearing 40 can be seen in particular. The bearing gap 39 of the radial slide bearing 31 is formed, on the one hand, by the circumferential surface 25A of the motor shaft 25 and, on the other hand, by the surface 33A of the through-hole in the bushing or sleeve 33 of the end wall 30 of the motor housing 20, the end wall 30 of the motor housing 20 defining an outer gap diameter of about 1mm, but the outer gap diameter may also be larger than this. In the present embodiment, the bearing gap 39 of the radial sliding bearing 31 has a gap converging from the proximal end to the distal end, a minimum gap width of 2 μm or less in the region of the leading end portion or the impeller-side end portion 39A of the gap 39. Preferably, the minimum gap width is between 1 μm and 2 μm. The maximum slit width is about 6 μm in the present embodiment, but may be larger. The length of the gap may range from 1mm to 2mm, preferably from 1.3mm to 1.7mm, for example 1.5mm, corresponding to the length of the radial sliding bearing 31. The surfaces forming the slits of radial sliding bearing 31 have a surface roughness of 0.1 μm or less.

Shaft 25 is preferably made of a ceramic material, most preferably Alumina Toughened Zirconia (ATZ) to avoid shaft breakage. ATZ has a relatively high thermal conductivity, since aluminum has a thermal conductivity between 30 and 39W/mK. The impeller 34 carried on the distal end of the shaft 25 is preferably made of a material having an even higher thermal conductivity. In this way, heat generated in the very narrow gap 39 of the journal bearing 31 can be dissipated through the shaft 25 and the impeller 34 into the blood flowing along the outer surface of the impeller 34.

However, in an embodiment in which the impeller is made of a material having a low thermal conductivity, such as PEEK, or even in an embodiment in which the impeller is made of a material having a high thermal conductivity, as set out above, it is in any case advantageous to make the sleeve 33 in the end wall 30 of the housing 20 using a material having a high thermal conductivity, preferably a thermal conductivity of at least 100W/mK, more preferably at least 130W/mK, even more preferably at least 150W/mK and most preferably at least 200W/mK. In particular, the sleeve 33 may be a ceramic sleeve, more particularly made of sintered ceramic material. As a particularly preferred ceramic material, the sleeve 33 may contain or entirely consist of SiC, because of its high thermal conductivity.

While the entire end wall 30 may be formed as a unitary piece manufactured from a highly thermally conductive material, it may be preferred to assemble the end wall 30 from the sleeve 33 and one or more radially outer elements 33B that are themselves thermally conductive. This may be particularly important where the sleeve 33 is made of a brittle material such as SiC. Accordingly, the radially outer heat conducting element 33B is thermally conductively connected to the sleeve 33 and has a thermal conductivity itself, which is preferably higher than the thermal conductivity of the sleeve 33 and in any case at least 100W/mK, so as to ensure that heat from the sleeve 33 can be dissipated into the flowing blood through the heat conducting element 33B by thermal conduction and diffusion.

As can be further seen from fig. 3, the axial length of the end wall 30 of the housing 20 is relatively long compared to the prior art structure shown in fig. 2. More specifically, the path for blood to flow along the outer surface of the end wall 30 of the housing 20 is longer in the axial direction than in the radial direction. This provides a large surface area for heat transfer from the end wall 30 of the housing 20 into the blood flow. For example, blood flow may be directed outwardly along the end wall 30 of the housing 20 over a radial distance of between 0.5 and 1mm, preferably about 0.75mm, while flowing in an axial direction 1.5mm to 4mm, preferably about 3 mm.

As regards the bearing gap of the axial plain bearing 40, it is formed by an axially inner surface 41 of the end wall 30 and a surface 42 opposite thereto. The opposing surface 42 may be a portion of a ceramic disk 44 that may be seated on the motor shaft 25 distal to the rotor 26 and rotate with the rotor 26. A passage 43 may be provided in the bearing clearance surface 41 of the end wall 30 to ensure that the cleaning fluid flows past between the bearing clearance surfaces 41 and 42 of the axial slide bearing 40 towards the radial slide bearing 31. In addition to this, the surfaces 41 and 42 of the axial sliding bearing 40 may be flat. The bearing gap of the axial sliding bearing 40 is very small, being a few micrometers.

When the bearing gap surface 41 of the axial sliding bearing 40 is formed by the sleeve 33, as shown in fig. 3, and the sleeve 33 is made of SiC, the ceramic disc 44 forming the opposite surface 42 of the axial sliding bearing 40 is preferably made of alumina-toughened zirconia (ATZ). Alternatively, the opposite bearing gap surface 42 may be DLC coated or may likewise be fabricated from SiC.

The pressure of the purge fluid is adjusted so that the pressure drop along radial slide bearing 31 is preferably about 500mmHg or more to maintain a high axial purge flow velocity (≧ 0.6m/s) within the narrow 1-2 μm gap. The blood pump 10 may be operated using a flush fluid without heparin. The blood pump can be run even without any cleaning fluid for at least a few hours, if the cleaning fails.

Fig. 4A to 4C show a variant of the converging circumferential slit 39 of the journal bearing 31 which is delimited at the distal end of the blood pump housing 20. The arrows indicate the flow direction of the cleaning fluid with which radial slide bearing 31 is cleaned.

A first embodiment of a converging slit 39 is shown in fig. 4A. Here, the slots converge continuously, more specifically linearly, from the proximal end to the distal end, with the minimum slot width being precisely at the impeller-side end 39A of the slot 39.

The slits 39 in the embodiment shown in fig. 4B likewise converge continuously and linearly from the proximal end to the distal end towards the impeller-side end 39A of the slit 39, but the minimum slit width extends over part of the length of the slit 39 forming a cylindrical end section thereof. The cylindrical end section of the slot 39 as shown in fig. 4B is less prone to wear than the pointed end section shown in the embodiment of fig. 4A. In both embodiments the slits may optionally converge non-linearly, in particular convexly or, in other words, progressively decrease from the proximal end to the distal end.

While the convergence of slits 39 in the embodiment shown in fig. 4A and 4B is due to the tapering of opening 35 with a narrower diameter distal end than proximal end, fig. 4C and 4D relate to embodiments in which the convergence of slits 39 is achieved by the tapering of shaft 25. More specifically, the outer diameter of the shaft 25 extends in both cases towards the impeller-side end 39A of the slit 39. In fig. 4C, the outer diameter of the shaft 25 expands from an equal diameter shaft segment on the proximal side of the slit 39, which extends across the end of the slit 39 opposite the impeller-side end 39A of the slit 39, to a maximum outer diameter within the slit 39. In the embodiment shown in fig. 4D, the outer diameter of the shaft has a circumferential groove, which likewise extends through the end of the slot 39 opposite the impeller-side end 39A of the slot 39. In the illustrated embodiment, the diameter of the groove increases linearly from the proximal end to the distal end, so that the minimum gap is reached shortly before the impeller-side end 39A of the slot 39. However, instead of linearly converging slits 39, the diameter of the shaft 25 may increase, for example progressively towards the impeller-side end 39A of the slits 39.

The variations described with respect to the embodiment shown in fig. 4A-4D may be combined in any suitable manner, i.e., the converging slit 39 may be formed by both the tapered diameter of the opening through which the shaft 25 extends and the tapered shaft 25.

Fig. 4E to 4I relate to an embodiment of the distal radial bearing 31 of the pump optimized with regard to the ease of manufacture of the converging slit 39. In fig. 4E the bearing 31 is divided into two bearing

rings

31A and 31B, the distal bearing ring 31A in contact with blood having an opening of a smaller diameter than the opening of the proximal bearing ring 31B. The converging gap in fig. 4F is achieved by a circumferential groove 25B in the surface 25A of the shaft 25, the groove 25B having a simple curvilinear cross-section. The gap which converges in fig. 4G is likewise realized by a circumferential groove 25B in the surface 25A of the shaft 25, but here the groove 25B gives the shaft 25A conical axial cross section in the region of the gap 39. In fig. 4H the bearing 31 is formed by a stepped bore having a smaller diameter at the distal end in contact with blood compared to the proximal end of the slit 39, similar to the embodiment of fig. 4E. In fig. 4I, again, the bearing 31 is divided into two bearing

rings

31A and 31B, with the distal bearing ring 31A in contact with blood having a smaller diameter than the proximal bearing ring 31B. However, in this embodiment the proximal bearing collar 31B has a cylindrical inner surface, while the distal collar 31A has a conical inner diameter converging towards the impeller-side end 39A of the slit.

Claims

1. An intravascular blood pump comprising a rotatable shaft (25) carrying an impeller (34) and a housing (20) having an opening (35), wherein the shaft (25) extends through the opening (35), the impeller (34) being positioned outside the housing, the shaft and the housing having surfaces (25A, 33A) forming a circumferential gap (39) within the opening (35), wherein the gap (39) has a length and has a width with a minimum width located somewhere within 50% of an impeller-side end (39A) of the length of the gap (39) closest to the gap (39).

2. The intravascular blood pump of claim 1, wherein the minimum width is present at the impeller-side end (39A) of the slit (39).

3. The intravascular blood pump of claim 1 or 2, wherein the minimum width extends over 30% or less of the length of the slit (39).

4. The intravascular blood pump of claim 3, wherein the minimum width extends no more than 20% through the length of the slit (39).

5. The intravascular blood pump according to any of claims 1 to 4, wherein the length of the slit (39) is in the range from 1 to 2 mm.

6. The intravascular blood pump of claim 5, wherein the length of the slit (39) is in the range from 1.3 to 1.7 mm.

7. The intravascular blood pump according to any of claims 1 to 6, wherein the slit (39) continuously converges through at least a portion of its length until the slit (39) has the minimum width.

8. The intravascular blood pump of claim 7, wherein the slits (39) converge linearly through at least a portion of their length.

9. The intravascular blood pump according to any of claims 1 to 8, wherein the diameter of the opening (35) converges towards the impeller-side end (39A) of the slit (39).

10. The intravascular blood pump according to any of claims 1 to 9, wherein an outer diameter of the shaft (25) is enlarged towards the impeller-side end (39A) of the slit (39).

11. The intravascular blood pump of claim 10, wherein the outer diameter of the shaft (25) has a circumferential groove extending through an end of the slit (39) opposite the impeller-side end (39A) of the slit (39).

12. The intravascular blood pump of claim 10, wherein the outer diameter of the shaft (25) expands from a constant diameter shaft segment extending past an end of the slit (39) opposite the impeller-side end (39A) of the slit (39) to a maximum outer diameter within the slit (39).

13. The intravascular blood pump of any one of claims 1 to 12, wherein the minimum width of the slit (39) is 5 μ ι η or less.

14. The intravascular blood pump of claim 13, wherein the minimum width of the gap (39) is 2 μ ι η or less.

15. The intravascular blood pump of any one of claims 1 to 14, wherein the maximum width of the slit (39) is 15 μ ι η or less.